Vitamin D, Muscle, and Testosterone

My regular readers know I don’t put much faith in supplements.  I have a very short list of supplements that work, and I’m very skeptical of bodybuilding supplements in general.  But Vitamin D is one I think every trainee should consider taking.  Here’s an overview:

Vitamin d plays a crucial role building both bone and muscle. We synthesize it when our skin is exposed to sunlight.  We also get it from food (or supplementation, which I will discuss later).

Deficiencies are associated with obesity and weaker muscles–this correlation has been shown through many studies over the years.

Studies have also  shown a positive correlation between levels of vitamin d and sex hormones (both men and women).1  Supplementing with this micro-nutrient, for example, seems to raise testosterone levels in men who are deficient.2

Vitamin d deficiency is very common, probably affecting half of the world’s population.3  Americans are not exceptions to this statistic.  A 2010 study revealed that 24% of the subjects tested (90 young women in California) were deficient in vitamin d, and even more (59%) were at “insufficient” levels (< or = 29 ng/ml).  Those with low levels of vitamin d had a higher % of fat within their muscles (“muscle adiposity”).4

So let’s put all this together:

1. Vitamin d that plays a crucial role in both muscular strength, leanness, and optimum hormone levels (like testosterone).

2. There’s a possibility you are deficient in it.

Here are a few of the factors that would tend to affect your levels of vitamin d:

*Skin tone: melanin protects from sun damage but also limits synthesis (darker skin=higher risk for deficiency).

*Sun exposure: the amount time you spend in the sun, the climate you live in, and the season (summer vs winter) all affect how much vitamin d you produce.

*Age: our ability to produce this vitamin declines with age.


One study demonstrated supplementing with 800-1000 mg/day way sufficient to improve the strength and balance of elderly patients. 5 The study I quoted earlier (re: raising testosterone levels) used about 3,000 mg/day.  I doubt any adult would have any issues supplementing in the 1,000-3,000 range–the institute of medicine puts the upper level of recommended supplementation at 4,000 mg/day.6  Vitamin D-3 seems to be the best choice as in terms of the type/form of supplement. 7

I use the NOW Foods Vitamin D-3, Structural Support 2000 I.U., 240 Softgels, but any reputable brand would do.

Having said this, I’d highly recommend you ask your doctor for a blood test to know exactly what your blood levels are.  This is the only way to know for sure and develop a precise strategy (supplementation, etc).

1.Eur J Endocrinol. 2012 May;166(5):765-78. Epub 2012 Jan 24.  Vitamin D and fertility: a systematic review.

2. Horm Metab Res. 2011 Mar;43(3):223-5. Epub 2010 Dec 10. Effect of vitamin D supplementation on testosterone levels in men.

3. J Pharmacol Pharmacother. 2012 Apr;3(2):118-26. Vitamin D: The “sunshine” vitamin.

4. J Clin Endocrinol Metab. 2010 Apr;95(4):1595-601. Epub 2010 Feb 17. Vitamin D status and its relation to muscle mass and muscle fat in young women.

5. J Am Geriatr Soc. 2011 Dec;59(12):2291-300. doi: 10.1111/j.1532-5415.2011.03733.x. Effect of vitamin D supplementation on muscle strength, gait and balance in older adults: a systematic review and meta-analysis.

6. Institute of Medicine: Dietary Reference Intakes for Calcium and Vitamin D

7. J Clin Endocrinol Metab. 2011 Mar;96(3):E447-52. Epub 2010 Dec 22. Vitamin D(3) is more potent than vitamin D(2) in humans.

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